The present invention generally relates to portable lighting devices (e.g., flashlights) and, more particularly, to a lighting device using multiple light emitting diodes (LEDs) as the light source.
Many light illuminating devices, such as flashlights, typically employ an incandescent lamp as the light source. Light emitting diodes (LEDs) offer many advantages over conventional incandescent lamps. LEDs are durable, have a lamp life of about 8,000 hours; and because they operate at low current drains, the useful life of energy storage batteries powering LEDs is extended. Despite these advantages, there are certain aspects of LEDs which limit their usefulness in certain applications, such as in portable lighting devices. The best standard 5 mm white LEDs currently available on the market are typically rated at about 3.6 volts, 30 milliamps (mA), and produce less than four (4) lumens of light. In comparison, an incandescent lamp used in conventional lighting devices with a similar voltage rating will typically produce light output that can range from less than ten (10) lumens to greater than forty (40) lumens or anywhere in between.
A solution to overcome the limitation of the LED currently being investigated is to use multiple LEDs as the light source in the lighting device. Some portable lighting devices currently use up to ten (10), or even more, LEDs as the light source, which increases the cost of the lighting device. Additionally, the light rays emitted by each LED are dispersed (e.g., forty degrees), and simply using multiple LEDs as the light source does not cure this problem.
One further approach to the solution is disclosed in U.S. Pat. No. 5,174,649 which employs one or more LEDs that illuminate portions of a single refractive lens element having hyperboloidal surfaces which translate the LEDs emitted rays into substantially parallel beams within the single refractive lens element. Another approach employing multiple LEDs in a flashlight is disclosed in U.S. Pat. No. 6,485,160 which employs multiple reflector wells, each housing an LED and a lens. While such approaches provide some directivity and concentration of light rays emitted from multiple LEDs, drawbacks still exist. For example, the formation of a complex refractive lens element and the requirement of the multiple reflector wells add to the cost and complexity of the lighting device.
In view of these disadvantages, it would be desirable to have an LED-based lighting system for a portable lighting device, which emitted light in a directed and concentrated manner.